1. Field of the Invention
The present invention relates to an improved pinning field between a nickel oxide pinning layer and a pinned layer of a spin valve sensor and, more particularly, to a method of improving the pinning field when the nickel oxide pinning layer has been exposed to atmosphere before forming the pinned layer thereon.
2. Description of the Related Art
An exemplary high performance read head employs a spin valve sensor for sensing magnetic fields on a moving magnetic medium, such as a rotating magnetic disk or a linearly moving magnetic tape. The sensor includes a nonmagnetic electrically conductive first spacer layer sandwiched between a ferromagnetic pinned layer and a ferromagnetic free layer. An antiferromagnetic pinning layer interfaces the pinned layer for pinning the magnetic moment of the pinned layer 90xc2x0 to an air bearing surface (ABS) which is an exposed surface of the sensor that faces the magnetic medium. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetic moment of the free layer is free to rotate in positive and negative directions from a quiescent or zero bias point position in response to positive and negative magnetic signal fields from a moving magnetic medium. The quiescent position is the position of the magnetic moment of the free layer when the sense current is conducted through the sensor without magnetic field signals from a rotating magnetic disk. The quiescent position of the magnetic moment of the free layer is preferably parallel to the ABS.
The antiferromagnetic pinning layer is typically nickel oxide (NiO). It is important that a high quality interface be formed between the pinning and pinned layers for promoting a high pinning field therebetween. The pinning field is related to the aforementioned exchange coupling field. The antiferromagnetic pinning layer has magnetic spins that are oriented in the desired pinned direction of the pinned layer. When the pinned layer interfaces the antiferromagnetic pinning layer, or interfaces another ferromagnetic layer therebetween, the magnetic moment of the pinned layer is oriented in a direction which is parallel to the magnetic spins of the antiferromagnetic pinning layer at its interface. When the interface of the antiferromagnetic pinning layer is degraded by contamination or roughness the exchange coupling and the pinning field between the pinning and pinned layers is reduced. Unfortunately, contamination of a top exposed surface of the antiferromagnetic pinning layer can take place during the processes of making the read head. The pinned, spacer and free layers are thin layers, on the order of 20 xc3x85-50 xc3x85, 20 xc3x85-25 xc3x85 and 40 xc3x85-70 xc3x85, respectively. In contrast, the thickness of the first and second shield layers is typically 1-2 xcexcm , the thickness of the first and second gap layers is typically in a range 300 xc3x85-1000 xc3x85 and the thickness of the antiferromagnetic pinning layer is typically 425 xc3x85.
It is desirable to form the antiferromagnetic oxide pinning layer in a first chamber and then form the pinned, spacer and free layers in a second chamber. The reason for this is because sputtering chambers are optimized for different functions, such as rate of sputtering, type of sputtering and pumping parameters. The first chamber may be optimized with a high sputtering deposition rate for sputter depositing the thicker first gap layer and the antiferromagnetic pinning layer while the second chamber may be optimized with a low sputter deposition rate for depositing the thinner pinned, spacer and free layers. The reason that a low sputter deposition rate second chamber is employed for the pinned, spacer and free layers is so that the thicknesses of these layers can be precisely formed.
Unfortunately, when the wafer with the antiferromagnetic pinning layer is removed from the first chamber and placed in the second chamber, the antiferromagnetic pinning layer has a top surface that is exposed to the atmosphere. This exposure seriously degrades the top surface of the antiferromagnetic pinning layer causing a very poor exchange coupling between the pinning layer and the pinned layer that is sputter deposited in the second chamber. Accordingly, the top surface of the antiferromagnetic pinning layer is sputter etched in the second chamber to clean the surface before sputter depositing the subsequent layers. Even with the sputter etch cleaning the exchange coupling is not as good if the antiferromagnetic had not been exposed to the atmosphere and sputter etch cleaned.
When exchange coupling between the pinning and pinned layers is low the magnetic moment of the pinned layer can be easily rotated from a direction perpendicular to the ABS. During subsequent fabrication steps of the remainder of the read head and the write head, the pinned layer is subjected to magnetic fields that are directed parallel to the ABS. Further, after the completed magnetic head assembly is mounted in a magnetic disk drive the read head may be subjected to extraneous magnetic fields parallel to the ABS that have a field stronger than the pinning field Hp between the pinning and pinned layers. The extraneous fields can cause the magnetic moment of the pinned layer to switch from the pinned direction perpendicular to the ABS to some other direction. Accordingly, there is a strong-felt need for providing a method of promoting a strong exchange coupling field between a pinning and pinned layer when the pinning layer is exposed to the atmosphere prior to formation of the pinned layer on the pinning layer.
I have provided a method of making the pinning and pinned layers with a high exchange coupling therebetween even though the pinning layer has been subjected to the atmosphere such as when the pinning layer, after its formation in a first chamber, is relocated to a second chamber. The method is implemented after the pinning layer is relocated in the second sputtering chamber. In the second sputtering chamber the top surface of the pinning layer is sputter etched in order to clean its surface and remove any contamination. A second layer of nickel oxide (NiO) is then sputter deposited on the first portion of the nickel oxide pinning layer with a predetermined thickness. The preferred thickness is in the range of 20 xc3x85-100 xc3x85 with the best thickness of this range being 40 xc3x85. The thickness of the first portion of the nickel oxide (NiO) layer is typically 400 xc3x85. When the second portion of the nickel oxide pinning layer is 40 xc3x85 it is found that the pinning field (HP) between the pinning and pinned layers was even higher than the pinning field between these layers when the entire pinning layer was sputter deposited in the second chamber. This was a surprising result even though the main objective was to overcome the problem of atmosphere contamination of the pinning layer when the pinning layer was constructed in a first chamber and the pinned layer was constructed in a second chamber. It should be understood that the invention not only has application to construction of the pinning and pinned layers in first and second chambers but also has application to methods where a period of time passes after the construction of the pinning layer and before the construction of the pinned layer.
An object of the present invention is to improve the pinning field between a nickel oxide (NiO) pinning layer and a ferromagnetic pinned layer.
Another object is to provide a method of making a nickel oxide (NiO) pinning layer in a first chamber and making a ferromagnetic pinned layer in a second chamber wherein exchange coupling between these layers is not degraded by exposing the pinning layer to the atmosphere when it is relocated from the first chamber to the second chamber.
Other objects and advantages of the invention will become apparent upon reading the following description taken together with the accompanying drawings.